The present invention relates to a condenser microphone in which a diaphragm and a back electrode are disposed oppositely to each other, a back chamber to improve the characteristics of microphone frequency being formed at the side of that rear surface of the back electrode which is not faced toward the diaphragm.
Conventional condenser microphones of this kind comprise a diaphragm, a back electrode disposed under the diaphragm, a back-chamber-constituting plate disposed under the back electrode, a circuit assembling plate disposed under the back-chamber-constituting plate, a plurality of electronic circuit elements including a preamplifier attached to the upper surface of the circuit assembling plate, and a space between the back electrode and the back-chamber-constituting plate forming a back chamber.
Such conventional condenser microphone can advantageously obtain the optimum characteristics of microphone frequency response, since the back-chamber-constituting plate so disposed as to permit the distance between the back electrode and the back-chamber-constituting plate, i.e. the capacity of the back chamber, to be freely changed.
On the other hand, however, such conventional condenser microphones are deficient in that the microphone structure is complicated.
The electronic circuit elements are soldered to that lower surface of the circuit assembling plate to which such electronic circuit elements are not attached. This soldering lower surface is not faced toward the inside of the microphone or the back electrode, but is faced toward the outside with respect to the microphone. Thus, such a soldering lower surface is susceptible to adverse influences from external noise, and therefore should be covered with a shield plate.
Accordingly, in addition to the back-chamber-constituting plate, such a shield plate is necessarily required, thereby disadvantageously increasing the number of members constituting the microphone.
Conventional condenser microphones of another type are known in which the back-chamber-constituting plate in the conventional condenser microphone above-mentioned, is eliminated.
In such a condenser microphone, the back chamber is formed between the back electrode and the circuit assembling plate. Thus, such a condenser microphone is advantageously constructed in such a manner as not to require the back-chamber-constituting plate. However, due to the presence of the electronic circuit elements, the distance between the back electrode and the circuit assembling plate cannot be reduced below a predetermined distance, so that the capacity of the back chamber cannot be reduced below a predetermined value. Thus, there is a case where the optimum characteristics of microphone frequency response cannot be obtained.
Furthermore, such a conventional condenser microphone necessarily requires a shield plate, so that reduction in the number of members constituting the microphone and simplification of the microphone structure cannot be realized.